The PTP, STEP, Regulates Amphetamine Actions

描述（由申请人提供）：慢性间歇性暴露于兴奋剂药物会产生持续和进行性的行为变化，包括对随后药物挑战的反应。这种现象被称为致敏。虽然动物模型已经提供了有关致敏反应的初始生化变化的信息，但对随后的步骤知之甚少。

DESCRIPTION (provided by applicant): Chronic intermittent exposure to stimulant drugs produces persistent and progressive changes in behavior including responses to subsequent drug challenges. This phenomenon is termed sensitization. Although animal models have provided information with regard to the initial biochemical changes involved in sensitazation, less is known about subsequent steps. The present RO1 will investigate this question. Our laboratory has discovered a family of protein tyrosine phosphatases (PTPs) that are expressed within neurons of the CNS. This PTP, termed STEP, is highly enriched in the striatum, nucleus accumbens, amygdala, and the frontal cortices. We recently determined that STEP regulates the activity of the MAP kinase members, ERKI/2. STEP is itself regulated by dopamine and glutamate signaling. Dopamine stimulation leads to the phosphorylation of key regulatory residues and inactivates STEP. Glutamate signaling dephosphorylates and activates STEP. STEP thus acts as a switch that regulates the activity ERK1/2 and limits its ability to activate downstream substrates. We propose that STEP regulates the effects of amphetamine. It does so by controlling the activity of ERKI/2. Consistent with this hypothesis, preliminary data in rats demonstrate that STEP is phosphorylated after amphetamine treatment. The sites phosphorylated are key regulatory residues in a domain required for binding to the ERKs. When STEP is phosphorylated at that site, the ERK signaling cascade is sustained. We will conduct time-course and dose-response analyses with psychostimulants, and perform immunocytochemical and Western blot analyses to determine the patterns of p-ERK, p-STEP, p-CREB, p- Elk-1 and the immediate early genes c-fos, jun and AfosB. We propose that the duration that ERKI/2 remain active determines the pattern of gene expression. Functional studies will disrupt the ability of STEP binding to ERK or disrupt the ability of STEP to let go of ERK. This will be tested by using TAT-peptide technology that introduces protein sequences that either prevent STEP from binding to ERK or never let go of ERK. We show preliminary feasibility data on this approach. A complementary set of experiments will study the STEP knock-out mouse that we predict is hypersensitive to stimulant treatment.